Apparatus for evaporating liquids



June 7, 1960 E. H. PATTERSON APPARATUS FOR EVAPORATING LIQUIDS Filed Feb. 19. 1958 gow, Scotland, assignor to G; & L Weir Limited, Holm v1 I'I Foundry, Cathcart, Glasgow, Scotland, a company of Great Britain Filed Feb. 19, 1958, Ser. No. 716,090

Claims priority, application Great Britain Feb. 23, 1957 1 Claim. (Cl. 159-37) This invention relates to improvements in apparatus for evaporating liquids adapted to be incorporated in a plant for evaporating water in large quantities for industrial and domestic requirements.

The invention contemplates so arranging the heating surface in a submerged tube evaporator that the hydro static head effect, which must be considered when evaporating at low temperatures and small temperature differences, is virtually eliminated, thereby allowing a greater number of stages or effects to be arranged in a multiple effect plant with resultant maximum economical performance.

The raw water to be evaporated in the plant may be sea, river, or other water, containing a considerable amount of dissolved impurities. The most commonly used method of evaporating such water is to feed the water into an evaporator shell in which there is arranged a heating surface presented by copper tubes or coils into which steam is led under pressure and is condensed, the heat of such steam being transmitted across the heating surface to the raw water in the base of the shell, whereby to evaporate the raw water. The liquid or brine in the shell is maintained at a predetermined density by the discharge of a proportion of brine dependent on the quantity of the raw water fed into the evaporator shell.

As is understood, the depth of the tube bank, or heating element, in a submerged tube evaporator has a definite effect on the actual mean temperature difference, particularly at low evaporation temperatures, which mean temperature in turn determines the rate of heat transfer, and thus the total heating surface required. In fact, it

is this factor which in pres'entevaporator design limits the number of effects or stages in a multiple effect evaporating plant to little more than six effects.

Apparatus according to the invention includes a submerged tube evaporator consisting of a tray for liquid to be evaporated, horizontal steam and drain manifolds in opposed end walls of the tray, a weir in one longitudinal wall of the tray, a bank of parallel horizontal tubes located in the tray and connected to the manifolds, the common tangent plane to the outer surfaces of the tubes remote from the bottom of the tray touching the lip of the weir, and an inlet to the tray for liquid to be evaporated.

At low temperaturedifferences, the maximum temperature difference between the heating steam and the vapour from the raw water is made full use of without interference from hydrostatic head, thus allowing small temperature differences of the order of F. to function without interference. Multiple effect plants may therefore be designed with more than six stages, thereby ensuring maximum economy in operation, which in large plants for industrial and domestic requirements is of vital-importance. v i

Apparatus according to the invention is illustrated in the accompanying drawings which show an evaporator which reduces the hydrostatic head effect to a water head equal to the depth of one tube so that, instead of being limited to a of F. evaporator temperature ice difference in multiple effect submerged tube evaporators, temperature differences down to the order of 5 F. can be considered.

' In the drawings, Fig. 1 is a perspective view of a plurality .of superposed submerged tube evaporators; Fig. 2 =is.a plan of a single evaporator; Fig. 3 is an elevation of the evaporator; Fig. 4 is asection on the lines 4-4 of Fig. 2; and Fig. 5 is .a'fragmentary section on the line 5-5 of Fig. 2. H

Referring to Figs. 2 to 5 of the accompanying drawings, 4 and 7 denote, respectively, steam and drain manifolds in opposed end walls of a tray 17. A bank of parallel tubes 6 in the tray 17 is connected to the manifolds 4 and 7. Steam enters through an inlet 3 into the manifold 4 which distributes the steam to the tubes 6. The rawwater enters the tray 17 through an inlet 13, flows along a tray 14 and overflows from the tray 17 at a weir 15 the lip of which touches a common tangent plane to the outer surfaces of the tubes 6 remote from the bottom of the tray 14. When flowing along the tray 14, the water completely submerges the tubes 6. Part of the water heated by the steam flowing through and condensing in the tubes 6, is evaporated, the remainder of the water spilling over the weir 15 and being equivalent to the blow-down. The condensate from the tubes 6 enters the drain manifold 7 and is discharged through an outlet 9. 5 and 8, respectively, denote manifold covers.

Referring to Fig. 1, any number of ,evaporators may constitute an assembly, and any number of evaporators may be arranged in one unit, depending on the heating surface required. Steam enters a manifold 2 through an inlet branch :1 and is distributed to the steam manifolds 4 by branches 3.

The condensate drains from the manifolds 7 and discharges to a drain outlet manifold 10 through outlet branches 9. The raw water enters an inlet branch 11 to a feed manifold 12 and is distributed to the trays 17 through branches 13, which supply feed troughs 14 in each tray 17. The water spilling over the weirs 15- collects at the bottom of an evaporator chamber for the evaporators and is then discharged to waste or, in the case of multiple effect plants, to the evaporator chamber of the next evaporator stage, and is then discharged. to waste from the last effect, by means of a pump. The steam produced in the evaporating operation escapes from each of the trays 17, below the top tray into the evaporator chamber through elongated openings 16 provided by the cutaway sides of the trays.

The following advantages are realised by the construction according to the invention, viz:

Complete counter-current flow of steam and water is obtained.

The rate of heat transfer exceeds that hitherto obtained in submerged tube evaporators which, depending on their construction, have depths of tube banks up to and exceeding 3 to 4 feet.

Brine discharge control may be achieved automatically by sizing the weirs 15 correctly to suit any requirement.

The individual evaporators are so constructed that manufacture and assembly are simple matters and, when required, the evaporators may be removed from the evaporator chamber with the minimum of trouble.

High rates of heat transfer are obtained with low temperature difierences of the order of 5 F.

Multiple effect plants may be built with ten or more effects according to the desired economy in operation.

What is claimed is:

Apparatus for evaporating liquids including a plurality of submerged tube evaporators arranged in superposed relationship, each evaporator consisting of a tray for liquid to be evaporated, horizontal steam and drain manifolds in opposed end walls of said tray, a weir in one longitudinal wall of said tray, a lip on said weir, a bank of parallel horizontal tubes located in said tray and coimected to saidmanifolds, the common tangent vplane to the outer surfaces of said tubes remote from the bottom of said tray touching the lip of said weir, an inlet to said tray for liquid to be'evagoratemtheweirs bf 'saidfsuperpo'sed 5 evaporators being in a common'vertical plane so that the overflows from said weirs are merged togiv'e parallel evapo-rationjn said superposed evaporators} asteani manifold common to the steam manifolds of the individual evaporators, a drain manifold eommon to the drain mani- 10 folds of said individual evaporators, and a manifold common to said evaporators ior'feed'to the trays of liquid to be evaporated.

References Cited in the file of this patent UNITED STATES PATENTS 

